1976 450SE

[Labninja]

     I went to start my car this morning and I couldn't keep it running. It ran fine last night when I went out to eat now it will run but only with the starter engaged. I thought it might be out of gas since the gauge was low so I put 1.5 to 2 gallons in with no change.
     I was going to put injectors in it yesterday but never got to it due to time problems. I did put my hand on on an injector, cold enrichment maybe, (it looked like an electronic injector close to the distributor) when I did that I heard a click. I thought I might have just needed plugged in since when I wiggled it it didn't move.
     So is it out of gas or did my fuel puimp die? I'd appreciate if I at least something to check.

Thanks

[ramiro]

Running only with starter engaged could be a ballast resistor problem when the starter is engaged 1 resistor is bypassed to make the spark stronger , could also be the fuel pump switch on the air flow meter that also is bridged when the starter is engaged is the fuel pump running when you remove the connector from the switch ?

The injector at the distributor is the cold start injector ,it is only active when starting the engine and the temp es below ~ 10 C so there should be no clock from it when you touch it , you can try unplugging it the engine should run fine without out only the start should be harder but it is also possible that is leaking for that you have to remove it.

[Labninja]

     I finally had a warm day, I pulled the plug to the fuel pump switch and the fuel pump runs. The car started for a few minutes then died. I put another 4 gallons in to be sure it wasnt a low fuel thing and it started and ran for 5-10 minutes then it just shut off. No sputter just off. The fuel pump runs with the switch unplugged (never shuts off) and not with it plugged in. Now it only fires with the key on again, so back to the same.
     So, is that what the switch is supposed to do?

[rumb]

Let's backtrack and have you describe your car - how long you have had it, any other issues, has it worked just fine for a long time before this? Has the car sat for a long time?  When were all the fuel filters last changed? The one by the pump and the one in the gas tank. What is the output of the fuel pump? (x liters/min). How old is the fuel pump?

Basic troubleshooting:  1. when it doesnt run, is there spark at the spark plugs? 2. if you crack open a fuel line at an injector does gas come out?  -

What does the cap and rotor look like?  same with spark plugs.

Further troubleshooting will require a fuel pressure gauge set - needed for basic understanding of your fuel system health.


"will run but only with the starter engaged."
so basically it doesnt run at all.  You are just turning the engine over making it seem it's running, but it's not?

[ramiro]

Here is the factory explanation for the fuel pump switch https://handbook.w116.org/cd/Engine/107/M117_45/073-165.pdf but if the engine is not running with the fuel pump running the problem is elswhere.

Atleast now we now that the fuel pump works , so if it really only runs when the startet is engaged maybe you ignition switch is broken , you can test that by checking the voltage on the ignition coil while the ignition is on it should be ~ 4.5 volts , here is the factory manual for the ignition system : https://handbook.w116.org/cd/Engine/107/M117_45/15-530.pdf .
Maybe your engine is running super rich and  fouled the plugs , when the starter is engaged the ignition bridges on balast resistor to have more power maybe that's enough to let it running with fouled plugs.

[Randys01]

it runs for awhile then stops seems to be the theme here.

Without any test gear try running the pump for 5 mins into a container.see if it conks out when it gets hot..............measure the fuel volume..about  1 litre per 30 sec.

if this is all good you can rule out pump,,filter andb accumlator.., then u can concentrate on the engine end.

[Labninja]

Let's backtrack and have you describe your car - how long you have had it, any other issues, has it worked just fine for a long time before this? Has the car sat for a long time?  When were all the fuel filters last changed? The one by the pump and the one in the gas tank. What is the output of the fuel pump? (x liters/min). How old is the fuel pump?

Basic troubleshooting:  1. when it doesnt run, is there spark at the spark plugs? 2. if you crack open a fuel line at an injector does gas come out?  -

What does the cap and rotor look like?  same with spark plugs.

Further troubleshooting will require a fuel pressure gauge set - needed for basic understanding of your fuel system health.


"will run but only with the starter engaged."
so basically it doesnt run at all.  You are just turning the engine over making it seem it's running, but it's not?

    From what I've read I was leaning toward a fuel pump/filter, I was just hoping not to have to do it.

I've owned it for about a month.

It ran as good as  you could expect but had a very high idle. I plugged several vacuum leaks and that helped but it would still idle above 1000rpm until almost completely up to temp then it would slow.
At lower idle it's obviously intermittently missing out. I bought injectors,seals, and the cups but hadn't put them in before it decided it didn't want to start.

I drove it home 2 hours from picking it up and about 2 hours to see family and to work for 3-4 weeks with nothing major wrong.

It was supposedly was stored inside for up to the last 15 years, which I tend to believe and is supposed to have been driven "About 200 miles a month". I think 200 a year is more accurate but what are you goig to do...

Very few maintenance records so I assume the pump and filters were done about 45 years ago, but even if they were new when parked they are at least 15 yrs. old.

I haven't checked the pump out put because frankly I didn't think about it.  I will now though.

Spark is good, a basic change of plugs etc wouldn't kill it.

It does try to start with the key as it turns faster than with the coil wire off, it just won't continue.

I will try running the pump into a container as suggested, at least I'd have confirmation. A new fuel pump/filter/accumulator couldn't hurt one way or the other though.

Thanks for the help everyone!


     

[rumb]

Check you WUR, warm up regulator. Lots of posts here on that subject and good youtube vidios.

CIS is the sum of all parts involved.

[Randys01]

Without any test gear he is a bit hamstrung but a simple volume test over 5 mins could eliminate a few things.
Again the WUR is always a candidate but you need a fuel press gauge.  It is theoretically possible to choke the fuel supply if the control pressure rises too far when hot but I've never met one yet that far gone.
Once again cranking up an old car that has been sitting around  only reinforces the case for a zero based approach to remedy, as it is almost impossible to pick an "eeny meeny miny mo" hot spot.

[CMS]

The key pickup from the posts I've read is the car running for approx 5 mins then cutting out.

This sounds like an issue with voltage.
Check your coil, ballast resistors and ignition leads.